Tuberculosis is a major cause of mortality and morbidity worldwide and more so for developing countries like India. The disease is caused by Mycobacterium tuberculosis. The organism is weekly gram-positive and resists decolorization while stained with an acid-fast stain. It spreads through airborne route and primarily affects the lung, however almost any body organ can be affected by tuberculosis. The lymph node has been one of the most common extra-pulmonary sites of involvement.

Bacille Calmette-Guérin (BCG) is a live attenuated vaccine used against tuberculosis since 1921. The BCG vaccine is derived from Mycobacterium bovis. Most of the BCG vaccine used globally is derived from four strains which include Pasteur strain 1173, Danish strain 1331, Glaxo strain 1077, and Tokyo strain 172. WHO recognize Tokyo 172 strain as a reference strain and recommend BCG to all newborns under the expanded programme of immunization for developing countries in 1974 [1]. The vaccine has questionable efficacy for primary prevention and re-infection of tuberculosis but its role in preventing severe complications of tuberculosis like miliary/disseminated tuberculous infection and tuberculous meningitis is well established [2].

The vaccine has been part of India's universal immunization programme considering tuberculosis being an endemic disease. As per the national immunization schedule the vaccine is administered at birth or earliest possible age till 1 year of age. In India, the vaccine is administered intradermally in the left upper arm near the insertion of the deltoid muscle; however this is not universal practice worldwide [3].

After administration, the bacteria of BCG vaccine multiply locally and are transported through lymphatic to regional lymph nodes. The BCG vaccine induces a delayed type of hypersensitivity response after 4–8 weeks of inoculation similar to tuberculosis. So the reaction at the site of inoculation and regional lymph node together constitute the primary complex of BCG. This phenomenon is very similar to a primary complex of tuberculosis [4,5].

Because of the hypersensitivity response, the general reaction to the BCG vaccine is induration and ulceration at the site of inoculation and enlarged ipsilateral lymph nodes. At the site of vaccination, ulceration was healed by a small scar. The vaccine is remarkably safe, although serious complications like osteomyelitis or disseminated BCG infection have been reported; they are rare and mainly related to some form of immune deficiency disorder. However, palpable enlarged regional lymph nodes are the most frequent minor complication of the BCG vaccine. Enlarged regional lymph nodes can sometimes become palpable. The term BCG lymphadenitis is used when the enlargement is a cause of clinical concern [2,6]. These lymph nodes are subjected to fine needle aspiration cytology. The study is aimed at describing the cytological spectrum of BCG lymphadenitis and its overlap with tuberculous lymphadenitis.